Adjunct processors are used in conjunction with telecommunications switching systems to provide to users telecommunications features and services that the switching systems and their intelligence (i.e., their control processors) are not designed to provide. A well-known illustrative example thereof are voice-mail systems. The adjunct processors are interfaced to users through the switching systems, and hence the control processors of the switching systems and the adjunct processors must have a capability of communicating with each other. The communications connections between the switching systems and the adjunct processors are typically accomplished through special control links. Illustrative examples thereof include the SMSI, DCIU, and ASAI links of AT&T PBXs. Consequently, in order for a switching system to be usable with an adjunct processor, it is generally required that the switching system provide and support the special control link.
From a cost standpoint it is desirable to physically incorporate the adjunct processor into the switching system. This eliminates the cost of a separate cabinet for the adjunct processor. It also eliminates the need for long cables and associated circuitry (e.g., amplifiers) for interconnecting the switching system and the adjunct processor. Furthermore, it often allows the adjunct processor to be powered from the power supply of the switching system, thereby eliminating the need for a separate adjunct power supply. An illustrative example of such a physically-incorporated adjunct processor is disclosed in U.S. Pat. No. 4,967,408. The incorporated voice-mail system disclosed therein has the additional advantage that its voice ports connect directly to the internal communications bus of the switching system, thereby eliminating the need for line-interface circuits for the voice-mail system voice-ports. Nevertheless, even when so physically incorporated into the switching system, the adjunct processor requires a special control-link connection to the control processor of the switching system.
Some arrangements for connecting an adjunct processor to a switching system have been proposed that avoid the need for a special control link. An illustrative example thereof is disclosed in U.S. Pat. No. 4,873,718. Therein, a voice-mail system is interfaced to a switching system through a digital feature-telephone set. The feature-telephone set is conventionally connected to the switching system by means of one or more digital telephone lines and digital line-interface circuits. The voice-mail system monitors the display of the feature-telephone set to obtain control information from the switching system, and activates keypad signals on the feature-telephone set to provide control information to the switching system.
Unfortunately, an arrangement of this nature does not facilitate incorporation of the adjunct processor into the switching system. Quite the opposite: it requires a complex interface arrangement comprising a digital line-interface circuit, a digital telephone line, a digital feature-telephone set, and telephone-set display-and keyboard-interface circuitry, to permit the adjunct processor and the control processor of the switching system to communicate with each other. Whatever advantage is gained by elimination of the special control link is offset in large measure by the cost and bulk of this additional interface equipment.